Microtubules and Tubulin

Microtubules

a network of filaments that extend from the centrosome to the cell peripherary

Microtubule made up of

repeating units of tubulin dimers, composed of alpha and beta tubulin

Protofilament

Non-covalently bound alpha and beta tubulin in a linear chain that has structured polarity

Microtubule structure

long, hollow cylindrical structure, straighter and more rigid than actin filaments

Nucleation

does not occur spontaneously and is carried out in a microtubule organising centre or centrosome

Gamma-tubulin ring complex

ring-shaped structure composed of gamma-tubulin that acts as an initiation site for microtubule growth

Gamma TuRC nucleation

Tubulin dimers associate with the ring complex at a specific orientation with the minus end bound to the ring and the plus end extending out into the cell

Centrosome structure

A pair of centrioles surrounded by a fibrous matrix with hundred of gamma TuRC’s on the surface allowing for microtubule growth out into the cell

Microtubule tracks

Microtubule extensions into the cell create tracks that allow for vesicle and organelle movement around the cell

Dynamic instability

repeated sequence of rapid microtubule growth from the centrosome followed by a rapid shrinkage phase- catastrophe

What is responsible for the pattern of dynamic instability

The rapid hydrolysis of GTP-bound tubulin

EB1

a protein that binds to a microtubule at the GTP cap

Vesicles

Use energy from ATP hydrolysis to travel along microtubules carrying their cargo

Kinesins

motor proteins that move along the cytoplasmic microtubules away from the centrosome toward the plus end

Dyeins

Motor proteins that move along the cytoplasmic microtubules towards the centrosome and the minus end

Organelle movement

When ATP is added as a fuel source some organelles bind microtubules and move along the tracks by motor proteins